#include <stdio.h>
#include <string.h>
#define N 81
void main()
{
    int i, j, k, flag;
    char str1[N], str2[N], str3[N];
    printf("Please input the first string:");
    gets(str1);
    printf("Please input the second string:");
    gets(str2);
    k = 0;
    for (i = 0; str1[i] != '\0'; i++)
    {
        flag = 1;
        for (j = 0; str2[j] != '\0' && flag; j++)
            if (str1[i] == str2[j])
                flag = 0;
        if (flag)
        {
            str3[k] = str1[i];
            k++;
        }
    }
    str3[k] = '\0';
    printf("The third string:");
    puts(str3);
}